Degradation of natural rubber (NR) during processing was investigated through NMR spectroscopy. Various commercial rubbers were used in the present study such as Pale Crepe (PC), Rubber Smoked Sheet (RSS 3), Technically Specific Sheet (TSS 8^®), Standard Thai Rubber (STR 5L), Standard Vietnamese Rubber (SVR 10) and Standard Malaysian Rubber (SMR 20). As-cast films of the rubbers were prepared by solution casting method and followed by purification by acetone extraction. Chemical structures of the rubbers were elucidated through ¹H, ¹³C-NMR, and DEPT spectroscopy. The ¹³C-NMR signals at 39.8 and 40.0 ppm were assigned to the trans-1,4-isoprene unit in the trans-trans and cis-trans sequences, respectively, while the signals at 60.8 and 64.5 ppm were assigned to C 2 and C 3 of a cis epoxy group. The cis epoxy groups were identified for PC, STR 5L, RSS 3, TSS 8^®, SVR 10 and SMR 20, whereas the trans-1,4-isoprene units from cis-trans isomerization were detected for TSS 8^®, SVR 10 and SMR 20.

In this study, the distributive mixing performance of Dulmage screw (DS), which is a type of fin mixing screw for a single screw extruder, was evaluated experimentally and numerically and the distributive mixing mechanism was investigated. The performance of DS increased basically with increase of the screw rotation speed, but the performance decreased under certain extrusion conditions. In the fin section, the positions of pigment changed by the circulation flow inside the fin groove and the degree of the change depended on the screw rotation speed. On the other hand, in the torpedo section, the flow velocity of pigment in the circumferential direction showed distribution in the radial direction. Thus, the distances moved by each pigment in the torpedo section were different. Moreover, the size of these differences determined whether or not splits occurred in the distribution of pigment on the fin inflow surface in the next stage. Especially, the DS distributive mixing performance tended to increase when a lot of pigment was distributed on the flight surface. From these results, it became clear that the performance depends on the amount of pigment that is distributed in the radial direction on the fin outlet surface.